Media and other content—such as music, movies, and literature, among others—that may typically be distributed to a large number of destinations are commonly distributed in a digital format over the Internet or other remote electronic or wireless communication medium. One of the principal problems that distributors of digital content face is unauthorized copying and redistribution of protected digital content, commonly known as piracy. Because of the widespread piracy problems, many content distributors seek to minimize the financial impact of piracy by implementing traitor tracing in their content protection systems.
Traitor tracing is a mechanism that detects guilty users who have participated in a pirate attack when pirate evidences become available. Authorized receivers that distribute protected content outside of authorized distribution channels are considered to be traitors. Different tracing schemes are used for different types of pirate attacks. One particular pirate attack that is frequently used is a rebroadcasting attack, in which the attackers redistribute content encrypting keys or decrypted plain content in an attempt to remain anonymous. When the version of content is the same between all receivers, the encrypting keys cannot be used to identify the traitors in a rebroadcasting attack.
Conventional content protection systems attempt to detect such attacks by distributing many versions of the content and by using watermarking and encryptions on various segments of the content. The content protection systems assign different versions to different receiver systems. This aids in identifying the traitor computer systems that is the source of the pirate rebroadcasts of the protected content.
Once a rebroadcast pirate attack is found, and the traitor tracing scheme identifies a particular computer system or group of systems as responsible for the attack, the distributor may then revoke access to the content for the identified system(s) and/or institute legal proceedings against individuals involved.